Any more (two words) is reserved for the meaning even the smallest amount. In other words, when used as a determiner, the two-word spelling any more is used. Anymore (one word) is reserved for the meaning any longer. In other words, when used as an adverb, the one-word spelling anymore is used.

I WON'T BUY
ANY MORE
CORVAIRS
I PROMISE
or
I WON'T BUY
CORVAIRS
ANYMORE
I PROMISE

Any more (two words) is reserved for the meaning even the smallest amount. In other words, when used as a determiner, the two-word spelling any more is used. Anymore (one word) is reserved for the meaning any longer. In other words, when used as an adverb, the one-word spelling anymore is used.

I WON'T BUY
ANY MORE
CORVAIRS
I PROMISE
or
I WON'T BUY
CORVAIRS
ANYMORE
I PROMISE